A new microspectrophotometer will be constructed. It will be a photon counting, computerized instrument with data storage and new data processing capabilities that will surpass presently available equipment. With this new instrument we will be able to study visual pigment chemistry and physiology in single photoreceptors with faster scanning speeds, smaller absorbance changes and smaller areas than with our present instrument. Our future experiments will be directed toward the use of this new equipment for studies on single photoreceptors, small portions of retina, isolated membranes and extracts. Studies on membrane and rhodopsin turnover along with regeneration of visual pigments in vertebrate and invertebrate photoreceptors will be improved and extended as a result of the increased versatility and sensitivity of the new MSP. This new equipment will greatly increase our capabilities in microspectrophotometry of any pigment carrying membrane system in animals, plant, and bacterial cells.